A 49-year-old woman presents with nephrolithiasis and bone pain. Laboratory Investigations show markedly elevated serum levels of calcium and parathyroid hormone. Parathyroidectomy reveals a solitary mass lesion in the left inferior parathyroid gland. Which of the following conditions is the most likely cause of hyperparathyroidism in this patient? cause adenoma A. Diffuse parathyroid hyperplasia B. Nodular parathyroid hyperplasia C. Parathyroid carcinoma D. Parathyroid adenoma
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Answer: D. Parathyroid Adenoma
The correct answer is D, and the key clues in this case all point directly to a parathyroid adenoma:
Why This Is a Parathyroid Adenoma
| Clinical Feature | Explanation |
|---|---|
| Solitary mass in one parathyroid gland | Adenomas are almost always solitary; hyperplasia involves multiple glands |
| Markedly elevated PTH + calcium | Classic primary hyperparathyroidism pattern |
| Nephrolithiasis + bone pain | Classic downstream effects of excess PTH ("bones, stones, groans, moans") |
| Left inferior parathyroid only | Hyperplasia and carcinoma rarely present as a true solitary lesion |
Why the Other Choices Are Wrong
- A. Diffuse parathyroid hyperplasia - involves all four glands (multiglandular process); associated with familial syndromes like MEN-1 and MEN-2. A single gland removed would not resolve it.
- B. Nodular parathyroid hyperplasia - still a multiglandular process (chief cell hyperplasia in a multinodular pattern); not a solitary lesion.
- C. Parathyroid carcinoma - rare (~1% of hyperparathyroidism cases); defined by invasive growth and/or metastasis. While it can present as a solitary mass, it is far less common than adenoma, and the question implies a straightforward resection without mention of invasion.
Epidemiology and Pathology (from Robbins)
"Parathyroid adenomas are almost always solitary... In contrast to primary hyperplasia, the glands outside the adenoma are usually normal in size or shrunken because of feedback inhibition by elevated levels of serum calcium."
- Robbins & Cotran Pathologic Basis of Disease
"The most common cause of primary hyperparathyroidism is a solitary parathyroid adenoma, followed by 4-gland hyperplasia and parathyroid carcinoma."
- Quick Compendium of Clinical Pathology, 5th ed.
Parathyroid adenoma accounts for ~85% of all primary hyperparathyroidism cases. The surgical finding of a single, well-circumscribed mass with the remaining glands being normal/suppressed is the hallmark.
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